1. Field of the Invention
This invention relates to the field of preparing poly(ether formal) glycols, and more specifically relates to synthesis of block poly(tetramethylene ether formal) glycols, block hybrid poly(ether formal) glycols, and oligomeric formal glycols from paraformaldehyde and, respectively, poly(tetramethylene ether) glycols, mixtures of poly(tetramethylene ether) glycols with polyethylene oxide glycols and/or polypropylene oxide glycols including substituted polyethylene oxide glycols, or alpha-omega diols such as monomeric 1,4-butanediol.
2. Description of the Related Art
Poly(tetramethylene ether) glycols, herein abbreviated as PTMEG, are commercially available and widely used as polyols along with a polyisocyanate and a chain extender in high performance polyurethanes. They are also used in polyetheresters and polyureas. PTMEG acts as an elastomeric soft segment in these products, while the chain extender and polyisocyanate or polyester contribute crystalline hard blocks to the final polymer structure. Several molecular weight ranges of PTMEG are made to cover a variety of end uses: Mn 650, 1000, 2000, and 2900 are typical. Molecular weights above 2000 cause the PTMEG to be difficult to handle because of its high viscosity. Further, even at 650 molecular weight, PTMEG is a borderline solid while higher molecular weights must be melted before use in most applications.
One approach to provide a lower melting modified PTMEG is to couple segments of the PTMEG with formaldehyde to break up the regular polyether structure as illustrated: EQU H[O(CH.sub.2).sub.4 ].sub.n OH+CH.sub.2 O+HO[(CH.sub.2).sub.4 O].sub.n H.fwdarw.H[O(CH.sub.2).sub.4 ].sub.n OCH.sub.2 O[(CH.sub.2).sub.4 O].sub.n H+H.sub.2 O
Also, 3 moles of PTMEG+2 moles of formaldehyde should yield EQU H[O(CH.sub.2).sub.4 ].sub.n OCH.sub.2 O[(CH.sub.2).sub.4 O].sub.n CH.sub.2 O[(CH.sub.2).sub.4 O].sub.n H+2H.sub.2 O.
These block PTMEG formal glycols, block hybrid poly(ether formal) glycols, and oligomeric formal glycols are characterized by lower crystalline melting points and lower viscosities than the corresponding PTMEG of similar molecular weight indicating a more random arrangement of the backbone structure of the glycols, and thus making these products easier to handle in their manufacture, shipping, storage, and processing in further reactions. Also included is a polymer of the formula: EQU H[O(CH.sub.2).sub.4 ].sub.a (OCH.sub.2).sub.b [O(CH.sub.2).sub.4 ].sub.a (OCH.sub.2).sub.b [O(CH.sub.2).sub.4 ].sub.a OH,
where the "a" components are derived from poly(tetramethylene ether) glycols of 650-3,000 Mn and "b" components are derived from formaldehyde or paraformaldehyde and may represent 0-3 or more (OCH.sub.2) formaldehyde linkages.
The invention relates to modification of poly(tetramethylene ether) glycols (PTMEG) to improve low temperature flexibility, alter hydrophilic/hydrophobic character, and affect water vapor transmission of the final polymers including polyurethanes, polyureas and polyetheresters made by incorporating the modified PTMEG. In addition, the modified poly(tetramethylene ether) glycols have lower melting points and lower viscosity than PTMEG of corresponding molecular weight, thus making easier handling of the materials in their manufacture, shipping, storage, and further reactions.
Some potential uses for the new oligomeric formal diols require further purification, for example to reduce trace impurities interfering with accurate molecular weight determination of the product, and to reduce the color of the oligomeric formal diols and their derived end-use polymers. A purification procedure in which the crude formals are treated with an aqueous calcium hydroxide solution, under conditions of steam distillation purging to destroy color-forming formaldehyde residues is an integral part of the preparation of the high quality formal glycols of this invention.
3. Description of the Prior Art
"Oligomeric Formal Diols of Poly(tetramethylene ether) Glycols and Polyurethanes Therefrom" is the subject of Pechhold U.S. Pat. Nos. 4,340,719 and 4,355,119. Pechhold prepared formal diols by coupling up to four PTMEG segments, each having a molecular weight of 1000-3000 with formaldehyde in the presence of a strongly acidic cationic ion exchange resin bearing --SO.sub.3 H groups, insoluble in the PTMEG, as catalyst. Rohm & Haas "Amberlyst" XN-1010 was satisfactory. The reaction medium was an aromatic hydrocarbon (toluene) at reflux temperature (110.degree. C.). Any water liberated by the coupling reaction was distilled off. The reaction vessel was then cooled, the contents were filtered to remove the catalyst, and toluene was stripped using a rotary evaporator to leave the oligomeric formal glycol.
For some applications, the oligomeric poly(tetramethylene ether formal) glycols so prepared require further treatments to satisfy commercial end use requirements.
British Patent 850,178 (Hudson Foam Plastics Corporation), Sep. 28, 1960, claims "A process for producing polymeric formals having a molecular weight of at least 1270, a hydroxyl number of less than 200 and terminal hydroxyl groups, comprising reacting a hydroxyl compound [one or more hydroxyl-terminated glycols] with formaldehyde in the presence of an acidic catalyst and separating the evolved water by the application of vacuum to the reaction mixture, the process being carried out at temperatures not exceeding 130.degree. C. and the reaction being continued until the desired degree of polymerization has been attained."
Page 1, line 63 states: "Thus, for example, under preferred conditions of the present invention, tetramethylene glycol gives rise to a reaction product including from 70 to 80% polymer and from 20 to 30% of a cyclic monomer having a boiling point of 116.degree.-117.degree. C. at 775 mm. of mercury. Glycols with more than four atoms between the hydroxyl groups result in reaction products having even larger proportions of polymer and correspondingly less monomer."
Published Japanese Patent Application 18598/75 to Nippon Soda Company broadly discloses reacting a polyetherpolyol with formaldehyde in the presence of sulfuric or phosphoric acid catalysts, and suggest that Friedel-Crafts catalysts can generally be used. The products were evaluated for preparation of both soft and hard polyurethane foams.
Chang et al., U.S. Pat. No. 3,959,277, May 25, 1976, point out that polyformals from alpha, omega-diols having at least 4 carbon atoms in a single chain are greatly improved for use in polyurethanes if the polyformal has a low methylol end-group content by treatment with alkali metal sulfite or bisulfite. The alpha, omega glycols of the examples are 1,6-hexanediol and thiodiethanol. 1,4-Butanediol and diethyleneglycol are listed as suitable co-monomers. In the best examples the methylol end group concentration was of the order of 2%. The methylol end-group content of the present poly(alkylene ether formal) glycols is believed to be essentially zero.
Cyclic and polymeric formals from alpha, omega-diols and formaldehyde were also investigated by Hill and Carothers, Journal of the American Chemical Society, Vol. 57, pages 925-928 (1935), and by Schonfeld, Journal of Polymer Science, Vol. 59, pages 87-92, (1962). Ethylene glycol, trimethylene glycol, and 1,4-butanediol yield the 5 member ethylene formal, the 6 member 1,3-dioxane (trimethylene glycol, and 1,4-butanediol yield the 5 member ethylene formal, the 6 member 1,3-dioxane (trimethylene formal), and the 7 member tetramethylene formal; all of these were isolated. Other monomeric formals made include the 8 member pentamethylene formal. The 9 member hexamethylene formal, the 12 member nonamethylene formal, the 13 member decamethylene formal, the 17 member tetradecamethylene formal, and the 21 member octadecamethylene formal. Attempts were made to polymerize these cyclic monomers at 150.degree. C. in the presence of a trace of sulfonic acid. The 6 member ring trimethylene formal could not be induced to polymerize. However, the monomer tetramethylene, pentamethylene, and triethylene glycol formals quickly became more viscous under the polymerization conditions.
The polyformal glycol from 1,4-butanediol and paraformaldehyde of this invention contains a portion of the formal --O(CH.sub.2 O)-- units present in a block oligomeric structure --O(CH.sub.2 O).sub.n --. In the practice of this invention, the number of formal units engaged in blocks is 0.5 to 30% of all formal units present. While the latter percentage is known precisely from NMR (nuclear magnetic resonance) observation, the value of n in the blocks is indeterminate, as is also the number of blocks with n greater than 1.
The above new composition of matter sets the compounds of this invention apart from those claimed in the previous art of making poly(oxybutylene formal) glycols in which the polymeric species have been described as the regular polymer of what could be considered the monomeric 1,4-butanediol formal. ##STR1## Further, the polymeric material of this invention posses no terminal hemiacetal links as determined by the invariance of the NMR carbon 13 spectrum to reaction of the polymer with aqueous sodium bisulfite solution, a treatment known to show hemiacetal end groups if present as described by Chang et al., U.S. Pat. No. 3,959,277 above.
The presence of the polyformal block units in the above soft segment preparation is unexpected on the basis of the earlier art and, as a feature of which introduces chain disorder into the soft segment backbone, is a valued formal physical property which imparts liquidity to formals of higher molecular weight. The same disorder can impart improved low temperature performance to polyurethanes prepared from other poly(oxyalkylene formal) glycols.